Micro-organisms are vital for soil fertility and for the degradation of
organic matter and pollutants in soils and sediments. Due to their
function and ubiquitous presence the microflora can act as an
environmentally very relevant indicator of pollution. Microbial tests
should be used discriminatory for the establishment of soil and sediment
quality guidelines. This review gives an evaluation of microbial
toxicity tests and a novel method to derive quality guidelines. The
replacement of sensitive micro-organisms by different resistant species
can have serious ecological consequences. Some species become extinct
while others appear in bulging numbers. Adaptation of a community to a
pollutant must be considered as the very process which disturbs a
polluted ecosystem. The resistant micro-organisms often fail to perform
specific ecological functions. The occurrence of resistant species can
be used as a sensitive and ecologically relevant indicator for
deterioration from environmental pollution. Persistent toxic effects on
the microflora can be caused by zinc, cadmium and copper at concentration
levels lower than the current European Community limits. After the
evaluation of the tests, a novel method is described to derive soil and
sediment quality guidelines using microbial toxicity tests. Microbial
toxicity tests can be used for risk assessment because micro-organisms
are among the most sensitive organisms for the effects of
pollutants.

Micro-organisms are vital for soil fertility and for the degradation of
organic matter and pollutants in soils and sediments. Due to their
function and ubiquitous presence the microflora can act as an
environmentally very relevant indicator of pollution. Microbial tests
should be used discriminatory for the establishment of soil and sediment
quality guidelines. This review gives an evaluation of microbial
toxicity tests and a novel method to derive quality guidelines. The
replacement of sensitive micro-organisms by different resistant species
can have serious ecological consequences. Some species become extinct
while others appear in bulging numbers. Adaptation of a community to a
pollutant must be considered as the very process which disturbs a
polluted ecosystem. The resistant micro-organisms often fail to perform
specific ecological functions. The occurrence of resistant species can
be used as a sensitive and ecologically relevant indicator for
deterioration from environmental pollution. Persistent toxic effects on
the microflora can be caused by zinc, cadmium and copper at concentration
levels lower than the current European Community limits. After the
evaluation of the tests, a novel method is described to derive soil and
sediment quality guidelines using microbial toxicity tests. Microbial
toxicity tests can be used for risk assessment because micro-organisms
are among the most sensitive organisms for the effects of
pollutants.